Electric fuse with separate quartz fillers
having different grain sizes



Dec. 13, i966 F. J. KozAcK ELECTRIC FUSE WITH SEPARATE QUARTZ FILLERS HAVING-DIFFERENT GRAIN SIZES Flled July 26, 1965 .r .ow'oww 1...'. J... ...f L., .3. uw.

INVENTOR= FREDERICK J KOZACKA BYWM 1 ATTORNEY United States Patent C) This invention relates to electric time-lag fuses capable of rapidly interrupting major fault currents, and also capable of effectively interrupting relatively small overload currents, if such currents persist for relatively long periods of time.

One aspect of the problem underlying the development of such fuses is that of the choice of a suitable pulverulent arc-quenching filler. Arc-quenching fillers which are best suited for interrupting high currents are not well suited for interrupting relatively low currents. Compromises between various kinds of fillers are not acceptable where both high current interruption requirements and low current interruption requirements are high.

It is well known that fulgurite-forming quartz sand is a filler particularly effective for interrupting relatively high currents, and that non-fulgurite-forming pulverulent arcquenching fillers which evolve gases under the heat of electric arcs are best suited for interruption of relatively low currents. Consequently a type of fuses has been evolved and is widely used which includes both aforementioned types of arc-quenching fillers, and is, therefore, capable of effectively interrupting both relatively high currents and relatively low currents.

Such dual-filter-fuses tend to evolve relatively high pressures because of the presence of a gas-evolving arcquenching filler, and cannot be manufactured in small sizes on account lof this tendency.

' It is, therefore, one object of this invention to provide fuses capable of effectively interrupting both relatively high currents and relatively low currents, which fuses are not subject to the aforementioned limitation, i.e. which fuses can be built in small sizes, or sub-standard sizes.

One prior art dual-filler fuse is disclosed in United States Patent 2,594,315 to Frederick J. Kozacka, April 2, 1952, Current-Limiting Fuse, assigned to the same assignee as the present application. The fuse structures disclosed in the above patent are intended to be applied in circuits having a circuit voltage of about 1000 volts. While their axial length is relatively moderate considering the circuit voltage for which they are intended, their diameter is relatively large on account of the presence of a radially outer casing forming a venting chamber of decompression chamber, in addition to a radially inner casing for the fuse link, a quartz filler and a chalk filler.

It is a further object of this invention to provide electric fuses which perform .substantially in the same way as the aforementioned dual-iiller-fuses, but which avoid a chalk filler7 or like gas-evolving ller, and thus are not subject to the limitations of such fuses, including the provision of two casings of which one forms a venting chamber, or gas decompression chamber.

Itis another object of this invention to provide extremely compact fuses effectively interrupting relatively high currents and relatively low currents, which fuses are particularly suited for circuits having a circuit voltage in the order of 300 volts, or less.

I have discovered that the above objects can be achieved by filling the casings of fuses with two separate bodies of quartz sand, one of said bodies comprising relatively line quartz sand, finer than U.S. Standard Sieve Number 40, and the other of said bodies comprising relatively coarse quartz sand, coarser than U.S. Standard Sieve Number 20.

For a better understanding of my invention reference may be had to the accompanying drawing in which fusing point metal 7 is arranged FIG. 1 shows a fuse embodying this invention and iS substantially a section along 1-1 of FIG. 2; and

FIG. 2 is substantially a section along 2-2 of FIG. 1.

Referring now to the drawings, numeral 1 has been applied to indicate a tubular Casing of insulating material closed on the ends thereof by terminal elements. Each terminal element includes an inner cap 2 defining a recess 3 at the axially outer end thereof and rolled at the axially inner end thereof at 4 into a circular groove defined by casing 1. Each terminal element further includes an outer cap 5 mounted on the aforementioned inner cap 2. Reference numeral 6 has been applied to indicate a fusible element or fuse link of a metal having a relatively high fusing point, preferably silver or copper. Fuse link 6 interconnects conductively the terminal elements 2, 5; 2, 5 and has a plurality of serially related points of reduced cross-sectional area. Recess 3 is filled with solder connecting the ends of link 6 to caps 2. A link-severing relatively low on fuse link 6 off the center thereof. Link-severing metal 7 is preferably in the form of an overlay on link 6, but might also take other Well-known forms as, for instance, that of a rivet projecting through one of the perforations provided in link 6. Part 7 may be an alloy of tin of the kind widely used in the art for severing fuse links at the occurrence of relatively small, protracted overloads. The transverse partition 8 of insulating material, e.g. fiber, subdivides casing 1 into a relatively long compartment (left) and into relatively short compartment (right). The latter houses a link-severing metal 7. The first-mentioned compartment contains a relatively fine quartz sand filler F1, and the latter compartment contains a relatively coarse quartz Sand filler F2. The grain sizes of the aforementioned quartz sand fillers are relatively critical. Filler F1 must be finer than U.S. Standard Sieve Number 40 and filler F2 must be coarser than U.S. Standard Sieve Number 20. Filler F1 should preferably be quartz sand as fine as 50-70 U.S. Standard Sieve Number. Filler F2 should preferably be as coarse as lO-l6 U.S. Standard Sieve Number.

The above figures as to preferred grain sizes of the two bodies F1 and F2 of quartz sand are a result of many tests conducted with a wide variety of grain sizes.

If partition 8 is omitted and the entire casing 1 filled with quartz sand as fine as 50-70 U.S. Standard Sieve Number, the fuses perform satisfactorily on shortcircuit tests, but fail on tests with relatively small overload currents.

In a similar fashion, if partition 8 is omitted and the entire casing 1 filled With quartz sand as coarse as 10-16 U.S. Standard Sieve Number, the fuses perform satisfactorily on tests with relatively small overload currents, but fail on tests with short-circuit currents.

The preferred ratio of the volumes of the bodies F1 and F2 of quartz sand is 2: 1. This ratio may be changed within limits, but the volume of the body of ne quartz sand should always by far exceed the volume of the body of coarse quartz sand.

On occurrence of small protracted overloads an arc is initiated at the point where the relatively low fusing point link-severing metal 7 is located. Backburning then occurs in opposite directions, and the arc is extinguished at a total gap length which is less than that of the right compartment of casing 1. It is apparent from the above that filler F1 does not come into play on interruption of relatively small currents.

On occurrence of short-circuit currents series arcs are formed substantially simultaneously at all points of reduced cross-section of link 6, and both fillers F1 and F2 cooperate to establish the arc voltage required for currentlimiting interruption of the faulted circuit. The arc voltage across each point of break formed in filler F1 exceeds the arc voltage across each point of break formed in filler F2, yet the arc voltages across the points of break formed in filler F2 are a significant contribution to the total arc voltages required.

Having disclosed a preferred embodiment of the invention, it is desired that the same not be limited to the particular structure disclosed. It will be obvious to any person skilled in the art that many changes and modifications may be made without departing from the broad scope and spirit of the invention. Therefore it is desired that the invention be construed as broadly as possible, and that it be limited only as required by the prior state of the art.

I `claim as my invention:

1. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of terminal elements closing the ends of said casing;

(c) a ribbon fuse link of a metal having a relatively high fusing point and having a plurality of serially related points of reduced cross-sectional area conductively interconnecting said pair of terminal elements;

(d) a link-severing relatively low fusing point metal arranged on said fuse link off the center thereof;

(e) a transverse partition subdividing said casing into a relativcly long compartment and a relatively short compartment, said relatively short compartment housing said link-severing metal;

(f) a relatively ne quartz sand filler finer than U.S. Standard Sieve Number 40 in said relatively long compartment; and

(g) a relatively coarse quartz sand filler coarser than U.S. Standard Sieve Number 20 in said relatively short compartment.

2. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

ib) a pair of terminal elements closing the ends of said casing;

(c) a ribbon fuse link of a metal having a relatively high fusing point and having a plurality of serially related points of reduced cross-sectional area conductively interconnecting said pair of terminal elements;

(d) a link-severing relatively W fusing point metal arranged on said fuse link off the center thereof;

(e) a transverse partition subdividing said casing into a relatively long compartment and a relatively short compartment, said relatively short compartment housing said link-severing metal;

(f) a relatively line quartz sand filler finer than U.S. Standard Sieve Number in said relatively long compartment; and

(g) a relatively coarse quartz sand iller coarser than U.S. Standard Sieve Number 20 in said relatively short compartment.

3. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of terminal elements closing the ends of said casing;

(c) a ribbon fuse link of a metal having a relatively lhigh fusing point and having a plurality of serially related points of reduced cross-sectional area conductively interconnecting said pair of terminal elements;

(d) a link-severing relatively low fusing point metal arranged on said fuse link off the center thereof;

(e) a transverse partition subdividing said casing into a first compartment about 2/3 the total volume of said casing and into a second compartment about 1/3 the total volume of said casing, said second compartment accommodating said link-severing metal;

(f) a quartz sand filler of 50-70 U.S. Standard Sieve Number in said rst compartment; and

(g) a quartz sand filler of 10-16 U.S. Standard Sieve Number in said second compartment.

ReferencesvCted by the Examiner UNITED STATES PATENTS 1,239,876 9/1917 Burnham 200-120 1,278,893 9/ 1918 Eustice 200-120 1,618,251 2/ 1927 Wentz 200--120 2,135,166 11/1938 Bussmann 200-120 2,439,674 4/ 1948 Schuck 200-120 2,665,348 1/ 1954 Kozacka 200-120 2,960,589 11/ 1960 Salzer 200-131 3,007,019 10/ 1961 Kozacka 200-120 BERNARD A. GILHEANY, Primary Examiner.

H. GILSON, Assistant Examiner. 

1. AN ELECTRIC TIME-LAG FUSE COMPRISING IN COMBINATION: (A) A TUBULAR CASING OF INSULATING MATERIAL; (B) A PAIR OF TERMINAL ELEMENTS CLOSING THE ENDS OF SAID CASING; (C) A RIBBON FUSE LINK OF A METAL HAVING A RELATIVELY HIGH FUSING POINT AND HAVING A PLURALITY OF SERIALLY RELATED POINTS OF REDUCED CROSS-SECTIONAL AREA CONDUCTIVELY INTERCONNECTING SAID PAIR OF TERMINAL ELEMENTS; (D) A LINK-SEVERING RELATIVELY LOW FUSING POINT METAL ARRANGED ON SAID FUSE LINK OFF THE CENTER THEREOF; (E) A TRANSVERSE PARTITION SUBDIVIDING SAID CASING INTO A RELATIVELY LONG COMPARTMENT AND A RELATIVELY SHORT COMPARTMENT, SAID RELATIVELY SHORT COMPARTMENT HOUSING SAID LINK-SEVERING METAL; (F) A RELATIVELY FINE QUARTZ SAND FILLER FINER THAN U.S. STANDARD SIEVE NUMBER 40 IN SAID RELATIVELY LONG COMPARTMENT; AND (G) A RELATIVELY COARSE QUARTZ SAND FILLER COARSER THAN U.S. STANDARD SIEVE NUMBER 20 IN SAID RELATIVELY SHORT COMPARTMENT. 